Mammalian spermatozoa acquire the ability to fertilize eggs after leaving the testis and during their passage through the epididymis. We have observed that as bovine spermatozoa pass through the organ, their carnitine content increases ten-fold and their cAMP content doubles. The research proposed here will investigate the physiological significance of this accumulation of carnitine and cAMP during maturation in the epididymis. We will use rabbits, whose exact pattern of fertility development is known, to investigate whether the carnitine and cAMP content of spermatozoa taken from various regions of the epididymis is correlated with their fertility. We will also ascertain, both in vivo and in vitro, whether spermatozoa retained in certain regions of the rabbit epididymis accumulate carnitine and (or) cAMP concurrently with acquiring fertility. We will continue our inquiry into why mature spermatozoa of many species (man, monkey, cattle, pig, rat) contain extraordinarily high concentrations of carnitine. The involvement of carnitine in regulating the energy metabolism of spermatozoa, particularly glycolysis and pyruvate oxidation, will be studied in bovine, monkey and rabbit spermatozoa. Since acetylcarnitine, which is highly concentrated in epididymal fluids, has been proposed as an important substrate for epididymal spermatozoa, we also plan to study in vitro its oxidation by the spermatozoa of several species. We especially want to learn whether acetate transfer occurs at the plasma membrane. Finally, we would like to identify the biochemical mechanisms whereby spermatozoa accumulate carnitine and cAMP. The possibility that acetylcarnitine is accumulated at a faster rate than carnitine will be explored. The cAMP content of epididymal fluids will be measured and the activity of adenylyl cyclase activity in epididymal spermatozoa will be determined. Establishing the intrasperm localization of adenylyl cyclase and identifying the activators of the enzyme will be emphasized.